Preparation of an active olefin polymerization catalyst

ABSTRACT

A titanium catalyst for polymerization of olefins is prepared by reduction of TiCl 4  with a mixture of AlEt 2  Cl and AlEt 3 , where at high AlEt 3  to AlEt 2  Cl ratios the aluminum reducing agents are added to the TiCl 4  solution. The reduction is performed from -50° to 0° C in a hydrocarbon and the reduced titanium compound is activated by heating to a higher temperature and subsequently is used with a cocatalyst for polymerization of olefins.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is not formally related to any pending patent application or issued patent of this inventor.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to an improvement in the preparation of a Ziegler catalyst for the polymerization of olefins wherein the improvement involves a more ready control over the reduction of the catalyst component and consequently a better control over the particle size and composition of the catalyst.

2. Problem to Which Invention is Directed

TiCl₃ cocrystallized with AlCl₃ can be prepared by reduction of TiCl₄ with aluminum alkyl halides. It is desired in the industry to prepare catalyst samples where the individual catalyst particles have diameters greater than 12 microns and where the catalyst samples have a narrow particle size distribution. These goals can be achieved by using as a reducing agent AlEt₂ Cl or AlEtCl₂. Any attempts to use AlEt₃ lead to catalyst particles whose diameters are normally less than 3 microns. With AlEt₂ Cl or AlEtCl₂ as reducing agents, the aluminum chloride content in the catalyst product, TiCl₃.nAlCl₃, is higher than desired and may lead to catalysts of low activity. Catalysts with optimum aluminum chloride content, where n = 0.25-0.35, can be prepared using compounds such as AlEt₃ or trialkyl aluminum as reducing agents. As pointed out before, trialkyl aluminum reducing agents lead to fine catalyst particles.

3. Description of Prior Art

It is well known in the prior art that olefins such as ethylene, propylene or higher olefins (as well as diolefins) can be polymerized to polymers of medium and high molecular weight by contacting them with Ziegler catalysts. Of these many Ziegler catalysts, the composition of TiCl₃.nAlCl₃, where n is usually about 0.33, in conjunction with a cocatalyst, such as AlEt₂ Cl or AlEt₃, is most commonly used. The TiCl₃.nAlCl₃ can be prepared by various techniques of which the following two are the ones most commonly employed:

(a) reduction of TiCl₄ with aluminum

(b) reduction of TiCl₄ with aluminum alkyl halides

By proper manipulation of conditions in the latter reduction procedure, one can obtain catalyst samples whose particle size distribution is narrow and whose particle size (diameters) can be varied. Most commonly the reducing agent used for the reduction of TiCl₄ is AlEt₂ Cl as disclosed in British Pat. No. 1,139,450 assigned to Shell International Research, and South African Applications Nos. 67-7828 and 67-7829, assigned to Hercules Inc.

It is also well known in the prior art that TiCl₃ catalysts such as these, when heated to temperatures above 150° C, are converted from their β form to the more active α or violet form. As for example in U.S. Pat. No. 2,971,925 to Winkler et al and U.S. Pat. No. 3,261,821 to Vandenberg.

By the use of different reducting agents, catalysts of different compositions are obtained. Furthermore, the use of different reducing agents in the reduction of TiCl₄ under proper conditions may lead to catalyst samples with different physical properties. It is highly desirable to obtain catalyst samples with optimum catalyst compositions along with proper physical properties. It is toward this goal that this invention is directed.

The prior art on mixed alkyl reduction also includes the following:

U.S. Pat. No. 2,943,068 (Jan. 28, 1960), L. T. Eby et al, claims brown reduction product of TiCl₄ and AlEt₂ Cl/AlEt₃ for polymerization of ethylene. The product which becomes inactive on standing may be reactivated with AlEtCl₂. I claim very specific conditions to prepare a spherical reduction product which is purple for the polymerization of propylene.

U.S. Pat. No. 2,962,491 (Nov. 28, 1960), Mertzweiler, claims partial reduction of TiCl₄ with AlEt₂ Cl and AlEtCl₂. The mixture AlEt₂ Cl/AlEtCl₂ is entirely different and will give different results than AlEt₂ Cl/AlEt₃.

U.S. Pat. No. 3,108,973 (Oct. 29, 1963), Vandenberg, claims TiCl₄ reduced by AlEt₂ Cl or mixture of AlEt₂ Cl/AlEtCl₂ and activated in polymerization with mixture of AlEt₂ Cl/AlEt₃. Same argument as above applies. The mixture of AlEt₂ Cl/AlEt₃ used in polymerization would be expected to give different results than when used in reduction.

SUMMARY OF THE INVENTION

An improved polyolefin catalyst is prepared by reducing TiCl₄ with a mixture of AlEt₂ Cl and AlEt₃ instead of AlEt₂ Cl.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is an advantage of this invention that a catalyst for polymerization of olefins can be prepared which is highly active, highly stereospecific, and which has favorable physical properties, i.e. catalyst samples whose individual particles have a narrow particle size distribution and whose individual particles have diameters greater than 12 microns. This can be achieved by reducing TiCl₄ with a mixture of AlEt₂ Cl and AlEt₃. The AlEt₂ Cl tempers the high activity of the AlEt₃ reducing agent. The mode of mixing of the reagents is important to obtaining an acceptable final product.

In the reduction of TiCl₄ with aluminum alkyl halide, the nature of the aluminum alkyl halide determines to a great extent the composition of the solid catalyst. For example, according to equation 1, below,

    TiCl.sub.4 + AlEtCl.sub.2 → TiCl.sub.3 . AlCl.sub.3 + Et. (1)

AlEtCl₂ used as a reducing agent leads to a catalyst high in aluminum chloride content. The use of AlEt₂ Cl (equation 2) or AlEt₃ (equation 3)

    TiCl.sub.4 + 0.5 AlEt.sub.2 Cl→ TiCl.sub.3 . 1/2AlCl.sub.3 + Et. (2)

    TiCl.sub.4 + 0.33 AlEt.sub.3 → TiCl.sub.3 0.33 AlCl.sub.3 + Et. (3)

leads to catalysts lower in aluminum chloride content.

It is possible to change the composition of the solid catalyst by using an excess of reducing agent. A problem that is associated with this technique is that the catalyst particles decrease in size as the ratio of reducing agent to TiCl₄ is increased. There are several problems associated with using AlEt₃ as a reducing agent as opposed to AlEt₂ Cl or AlEtCl₂. First of all, it is a much more active reducing agent so that an excess of AlEt₃ will lead to overreduction of TiCl₃ to TiCl₂ which is a less stereospecific and less active catalyst. Secondly, the use of AlEt₃ as reducing agent leads to catalyst samples whose particles are very fine in size and consequently are undesired in many parts of the industry. While mixing TiCl₄ with AlEt₃ at very low temperatures, such as -75° C, and changing the mode of mixing from adding TiCl₄ to AlEt₃ or vice versa, one still obtains catalyst samples that are undesirable.

It has been found that when AlEt₂ Cl is mixed with AlEt₃ and this mixture of reducing agents is added to TiCl₄ at -30° C, acceptable catalyst particles are formed. The mode of mixing of components is important in situations where the AlEt₃ to TiCl₄ ratio is above 0.15. Thus as the examples will show, addition of TiCl₄ to mixtures of AlEt₃ and AlEt₂ Cl in these cases where the ratio is in excess of 0.15 will lead to catalyst samples wide in particle size distribution and heterogeneous in physical properties.

It is believed, although this invention should not be limited to this, that the addition of AlEt₂ Cl and AlEt₃ mixture to TiCl₄ at low temperature results in a rapid reduction of TiCl₄ by the minor amount of AlEt₃. Subsequently, AlEt₂ Cl coats the catalyst particles and proceeds to further reduce the adsorbed TiCl₄ at a slower rate. The adsorbed or complexed AlEt₂ Cl protects the reduced TiCl₄, TiCl₃ from further attack by freshly added AlEt₃. The AlEt₂ Cl mixed with AlEt₃ further tempers the reducing ability of the AlEt₃ through formation of an associated complex.

The invention is further illustrated in the following examples. Table I summarizes the reaction conditions and resulting compositions. The composition of the reducing mixture can be varied but beyond a certain concentration of AlEt₃ in the reducing mixture the mode of mixing of reagents becomes important.

The data in Table II illustrate that as the alkyl group content in the reducing agent, AlR_(n) X_(3-n), is increased from 1 to 3, the AlCl₃ content in the catalyst product is reduced. Furthermore, the activity data of the catalyst with different AlCl₃ contents, as seen in Table I, shows that near optimum catalyst activity is obtained where the aluminum content is near 0.25 to 0.35. This kind of catalyst composition in catalyst samples with the most favorable physical properties stated earlier, can only be obtained by using as a reducing agent, mixtures of AlEt₂ Cl and AlEt₃ according to this invention.

                                      Table I                                      __________________________________________________________________________     Reduction of TiCl.sub.4 with Mixtures of AlEt.sub.2 Cl and AlEt.sub.3                                                      Catalyst                                                    Catalyst  Stir-    Particle                                                                            Hep-                          TiCl.sub.4 AlEt.sub.2 Cl                                                                         AlEt.sub.3                                                                            Addition                                                                             Mixing                                                                             ring                                                                               Catalyst                                                                            Size tane,                         Run Vol.,                                                                             Moles                                                                              Vol.,                                                                             Moles                                                                              Vol.,                                                                             Moles                                                                              Ti Al Temp.,                                                                             Speed,                                                                             Size,                                                                               Distri-                                                                             Vol.,                                                                             Mole Ratio                 No. cc × 10.sup.3                                                                   cc × 10.sup.3                                                                   cc × 10.sup.3                                                                   to Al                                                                             to Ti                                                                             ° C                                                                         rpm microns                                                                             bution                                                                              cc TiCl.sub.4 :AlEt.sub.2                                                          Cl:AlEt.sub.3             __________________________________________________________________________     4271-13                                                                            75.sup.a                                                                          170.6                                                                              63.6.sup.b                                                                        102.4                                                                              23.7.sup.c                                                                        25.6   x  -30 250 15.5 Average                                                                             73 1:0.6:0.15                 4271-12                                                                            75.sup.a                                                                          170.6                                                                              63.6.sup.b                                                                        102.4                                                                              23.7.sup.c                                                                        25.6                                                                               x     -30 250 11-15                                                                               Wide 73 1:0.6:0.15                 4271-11                                                                            75.sup.a                                                                          170.6                                                                              68.8.sup.b                                                                        110.9                                                                              15.8.sup.c                                                                        17.06                                                                              x     -30 250 10- 21                                                                              Average                                                                             75 1:0.65:0.10                4271-10                                                                            75.sup.a                                                                          170.6                                                                              74.1.sup.b                                                                        119.4                                                                               7.9.sup.c                                                                        8.5 x     -30 250 20   Narrow                                                                              78 1:0.70:0.05                4060-42                                                                            75.sup.e                                                                          149 -- --  60.sup.f                                                                          60  x     -70 210 1.5-2.5                                                                             Narrow                                                                              -- 1:0:0.4                    4060-46                                                                            50.sup.a                                                                          114 -- --  45.7.sup.f                                                                        45     x  -70 240 1.8-7.0                                                                             Wide -- 1:0:0.4                    __________________________________________________________________________      .sup.a. 2.274 molar concentration in heptane.                                  .sup.b. 1.6106 molar concentration in heptane.                                 .sup.c. 1.079 molar concentraton in heptane.                                   .sup.e. 2.0 molar concentration in heptane.                                    .sup.f. 1.0 molar concentraton in heptane.                               

                                      TABLE II                                     __________________________________________________________________________                               Catalyst                                                    Reducing                                     Activity,                         Agent   Mole Ratio,                                                                               Particle Size,            gms PC.sub.3 =             Run No.                                                                               AlR.sub.n Cl.sub.3-n                                                                   TiCl.sub.4 :AlR.sub.n Cl.sub.3-n                                                          microns  Composition TiCl.sub.3 . nAlCl.sub.3,                                          n                gm TiCl.sub.3 . 2          __________________________________________________________________________                                                         hrs                        4060-46-2                                                                             AlEt.sub.3                                                                             2.5        1        0.35             31.7                       4121-58-2                                                                             AlEt.sub.2 Cl                                                                          2          27       0.50             19.2                       4121-79-2                                                                             AlEt.sub.1.5 Cl.sub.1.5                                                                1.25       30       0.62             16.5                       4122-10-2                                                                             AlEtCl.sub.2                                                                           0.67       50       1.0              18.7                       __________________________________________________________________________

It should also be noted that Japanese Pat. No. 9083-696 published on Dec. 18, 1972 also shows the reduction of TiCl₄ with mixtures of aluminum trialkyl and aluminum dialkyl chloride. However, this reference does not teach the use of very small quantities of aluminum trialkyl in the presence of the aluminum dialkyl monochloride. Furthermore this reference has no teaching with respect to the improved catalyst particle size and distribution that can be obtained in utilizing the very low quantities of the aluminum trialkyl which is taught by applicant.

The other patent of some significance is German DT No. 2342-416, published on Oct. 6, 1962. That patent teaches an initial reduction of TiCl₄ with 0.36 mols of aluminum triethyl over a long period of time followed by subsequent treatment with 0.73 mols of aluminum diethyl chloride over a long period of time followed by a final TiCl₄ treat. The net effect of the process is considerably different from that of applicant's since the quanity of aluminum triethyl used is much higher than that specified by applicant. It is clear from applicant's data that very small particle size TiCl₃ is formed from the initial reaction of TiCl₄ with the aluminum triethyl.

It is only after the subsequent TiCl₄ is added as the next to last step of the reaction that a reasonably large particle size is obtained. In contrast to the DT No. 2342-416 patent, applicant obtains excellent particle size and distribution without having to utilize a final TiCl₄ reduction step.

In any event, applicant's experiments and reductions to practice were carried out at dates much earlier than these patents' effective filing and publication dates.

Generally speaking, the mean particle diameter will be about as low as 10, and up to 200 microns, preferably 12 to 50 microns, and most preferably about 20 to 25 microns.

The general reaction conditions and equipment utilized in the technique of the invention, especially that of the examples, is disclosed in U.S. Pat. No. 3,905,915, which is hereby incorporated by reference in its entirety.

For the purposes of this invention, the term "alkyl" as used herein means a C₁ to C₁₂ aliphatic hydrocarbon group. The ethyl species is particularly preferred.

In general, it is recognized by the art that if the aluminum chloride content of a cocrystallized TiCl₃ aluminum chloride catalyst can be considerably reduced from its normal quantity to the 0.25 to 0.35 range results in considerably better catalyst.

If desired, the catalyst produced by the process of this invention can be additionally improved by treatment with a Lewis base, especially diisoamyl ether or n-butyl ether to extract residual titanium trichloride from the catalyst, followed by washing and activation by the use of TiCl₄.

The resulting catalyst can be used as is with a standard cocatalyst, or can be additionally made more active by utilizing a third component, such as another Lewis base in the polymerization reaction.

This approach is described in German patent DT No. 2457-278 which is incorporated herein in its entirety by reference.

Generally speaking, the mole ratio of aluminum trialkyl to titanium tetrachloride is from about 0.01 to 0.15, preferably about 0.05 to 0.15.

It should be further noted that the reducing agent, e.g. aluminum trialkyl and aluminum dialkyl chloride combinations, can be additionally complexed with various Lewis bases to further improve the titanium chloride catalyst produced. Thus, Lewis bases are complexed with the reducing agent. The preferred Lewis bases are ethers or thioethers which can be described by the formula ROR', RSR', where R and R' are hydrocarbon radicals containing from 1 to 15 carbon atoms, preferably R and R' are branched hydrocarbon radicals containing from 2 to 8, preferably from 4 to 6, carbon atoms.

The complexing agent is mixed with the reducing agent in the ratio of from 0.01 to 5:1, or preferably from 1.0 to 5:1, most preferably in the ratio from 1-2:1.

The details on utilizing a complexing agent complexed with the reducing agent to achieve improved reduction of TiCl₄ to TiCl₃ is described in detail in applicant's United States patent application entitled "Reduction of TiCl₄ with Reducing Agents Modified with Lewis Bases", Ser. No. 622,956 filed Oct. 16, 1975, which application is hereby incorporated by reference in its entirety in this instant application. 

What is claimed is:
 1. A process of preparing TiCl₃.nAlCl₃ catalysts where n = 0.25 to 0.35 having a mean particle diameter size of from 10 to 200 microns and narrow particle size distribution which consists of reducing TiCl₄ with a mixture of AlEt₃ + AlEt₂ Cl wherein the mole ratio of AlEt₃ to TiCl₄ is from 0.01 to 0.15:1 at a reduced temperature of from about -50° to about 0° C, gradually raising to an elevated temperature sufficient to convert the TiCl₃ .nAlCl₃ catalyst to the violet form.
 2. The process of claim 1 wherein said ratio is about 0.05:1.
 3. The process of claim 1 wherein said ratio is about 0.15:1.
 4. The process of claim 1 wherein said mixture of aluminum compounds is gradually added to said TiCl₄ over the space of about 0.2 to 10 hours at a temperature of from -50° to +50° C.
 5. The process of claim 1 wherein said titanium compound is added to said mixture of aluminum compounds over a space of from 0.2 to 10 hours at a temperature of from -50° to +50° C.
 6. The process of claim 4 which is carried out under constant stirring.
 7. The process of claim 5 which is carried out under constant stirring.
 8. The process of claim 1 wherein said mixture also is complexed with a Lewis base.
 9. The process of claim 8 wherein said Lewis base is R--O--R', wherein R and R' are alkyl groups having from 2 to 6 carbon atoms.
 10. The process of claim 9 wherein said ether is is diisoamyl ether. 